Carrier-wave transmission



J. S. JAMMER CARRIER WAVE TRANSMISSION Dec. 21 1926.

Filed July 25, 192s f 2 Sheets-Sheet 1 llllll..

/n Ven/0r: JacUb S Jammer by Vlmhmccccw r nl- @EEES Dec; 21 1926.

J. s. .uw/MER CARRIER WAVE TRANSMISSION Filed July 25, v1923 2 Sheets-Sheet 2 K h.. uw. h n wir@ T I M m w s E? it; IM l W U 1 1 i; NU v u/m THU fww .w ,Iii/.1 M m f BEES 1J@ Y n@ Q x N U n HJ--- Patented Dec. 2l, 1925.

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JACOB S. JAIMER, OF NEWT` YORK, N. YIASSIGN0R TO WESTERN ELECTRICCOMPANY INCORPORATED, OF N'EW YORK, N. Y., A. CORPORATIONYOF NEW YORK.

PATENTLaoFl-"lcs j CARRIER-WAVE TRANSMISSION.

Application led July 25, 1923. *Serial No. 658.629.`

This invention relates to carrier. Wave transmission'. Y Among the obJects of the invention are:

To provide in a multiplex carrier signal ing system an increase 1n the number of' signaling vchannels within the given frequency range.

signals may be transmitted simultaneously on the same carrier.

To provide in ,a multiplex carrier signaling system efficient inter-communicating means between the terminal and repeater 'stations To provide improved intercommunicating n'leans between the .terminal and repeater stations of a transmission system which will in no wise he affected by or'atlect the operation ofthe repeaters. t

To'provide for a plurality of multiplex carrier signaling systems efficient and economical attenuation indicating mechanism common thereto.

To provide efficient attenuation testing mechanism whereby each of a plurality of `carrier signaling systems may be automatically and successively tested.

In accordance with one feature of the invention, a multiplex carrier wave telephonesystem has associated "with one or more channels thereof telegraph transmitters for changing the magnitude of the carrier current in the channelswhereby telegraph receivers will respond thereto Without affecting the operation of the carrier telephone apparatus so that telephone and tele- `graph signals 'may be transmitted simultaneously on the same carrier. l I

According to another feature of the inventionlthe 'terminal and repeater stations of a carrier Wave signaling system are provided with sending and receiving apparatus for affording intercommunicationy between any two or all of said stations. v Such intercommunicating apparatus operates with carrier current of a frequency differing from that employed in the usual signalingchannels and entirely indepcndent'of the repeaters and the carrier Wave transmission apparatus 'of the usual channels of the system.

According to a further feature of the invention there is provided, at a Station where a plurality of carrier wave transmission systems terminate, an attenuation indicator which may be associated With` any one of such lsystems to vmeasure and Yindicate the attenuation thereof. This attenuation indicator is responsive to a pilot frequency which is clitferent'fromvthe usual'channel frequencies.

If the measured attenuation differs from -I the adopted standard by more than a. predetermined amount, d ue to line changes, a .signal 4is operated tov so indicate to the station attendant, who may then communicate with `the distant terminal and repeater attendants to make th'e appropriate adjustments to bring the-transmission back to the adopted standard. Apparatus is provided wherebythe attenuation indicator is autoi'natically and successively' associated with the various carrier Wave transmission systems to measure the attenuation thereof.

The invention will be described as applied t0 a multiplex carrier signaling transmission system, although it will be understood that it is not limited to suchfa system for some of the features thereof may find application in other forms o f signaling systems and in other-fields.

In the drawings:

Figs. 1 and 2, when placed end to end with Fig. 1 at the left, show diagrammatically a multiplex lcarrier telephone and telegraphl system provided with the intercommunicating channel and the attenuation indicator of' the invention, the indicator serving also for several other such systems, which are merely indicated.

F ig. 3 shows curves representing the magnitude and .form of the carrier and voice side band waves in the carrier telephone and telegraph System.

Fig. 4 shows the operating characteristics of the -rectifiers of the carrier telephone and telegraph system. y

The multiplex carrier telephone and telcgraph system of Figs. 1 and 2 comprises in general a main high frequency transn'lission 'line ML extending between terminal stations W and E and having internicdiate thc terminal stations a plurality 'ofvrepeatcr sta- 'tions It'.

loo

sion in one direction being grouped in a different frequency range from those employed :for transmission vin the opposite direction. The telegraph channelsaresuperposed upon the telephone channels in a manner to` be described and employ the same carrier 'frequencies respectively. l

An intercommunicating `channel IC for communciation between the repeater and terminal stations is associated with the multiplex carrier telephone and telegraph system. Thisintercommunicating system employs but one carrierV frequency, which is i differentfrom that of any of the telephone and telegraph channel frequencies. Preferably, the intercommunicating channel fre- ,quency is higher than that of any 'of the telephone and telegraph channel frequencies.

The multiplex vcarrier telephone and telegraph'system is also provided with a .pilotchannel for measuring and indicating the gain of the' transmission line and the apparatus associated therewith. T he pilot frequency is different from thefrequencies l5 of the telephone and telegraph channels and the intercommunicating channel.

The apparatus at the two terminal stations is' similar so that a description of the apparatus of one terminal will suffice.v

Terminal statonneultiplem carrier teepzonc amd telegraph system.

y The multiplex carrier telephone and telcgraph system has three or more telephone channels upon each of'which is superposed a telegraph channel arranged for twoway operation. Since the channels are alike except for the `constants of some of the apparatus thereof, due to the different frequen- 4" cies employed, it will be unnecessary to describe more than one such channel. v

I There is provided at the terminal station W, for example, three telephone channels, 1, 2 and 3, an intercommunicating. channel "15 IC, and a pilot channel PC, all of which are connected te the main line ML.

Telephone channelNo. 1 includes a transmitting channel TC1 and a receiving channel RC1, which are conj'ugately related to a low frequency telephone line L1 byl means of a transformer 5 and a balancing net work N. The telephone line L1 usually extends to and terminates at a `telephone switchboard (not `shown).

The'transmitting channel TC1 includes a modulator M1 and a transmitting band filter TBR. The modulator M1 may be of any wellknown type, such, for example, as the elecm tronic valve modulator of the three-electrode type disclosed in Fig. 42 of the article Carrier current telephony and telegraphy by Colpitts and Blackwell appearing in Transactions of theAmerican Institute of ElectricalEngineers, volumeAlO; l1921. Carrier current of the frequency assigned to this channel is supplied to the modulator M1 from a high frequency source 0,.l

The transmitting band filter TBI",l is of the type disclosed in U. S. patents to Campbell` Nos. 1,227,113 and 1,227,114 of May 22, 1917. 'This band 'filter isdesigned to pass currents of the carrier frequency assigned to key 6 the amplitude of the carrier current supplied to the modulator M1 is alternately reclluced from and, restored to its normal va ne.

Consequently the telephone signal; modulatedcarrler current output from the' modulator M1 is intermittently changed in amplitude during the transmission of telegraph slgnals. i i

The relative amplitudes of the carrierfre-l quency when the transmitting key 6 is open and closed is shown in Fig. 8. This figure also shows the amplitude of the voice or telephone side band currents.

The receivin channel RC1 includes a rei ceiving band lter RBFI,l a demodulator DMI, an amplifier A1, a low pass filter LPF, a high pass filter HPF, arectiier R1, and a Atelegraph receiving relay 8 which controls the usual telegraph sounder 9. The 'receiving band filter is of the type disclosed in the Campbell patents, supra 7 It is designedto pass currents of the carrier frequency assigned to this channel and of the frequencies within either the upper or lower side band thereof and to suppress currents of all other frequencies. The demodulator DM1 and the amplifie il'may be of any well known type, such, for example, as those disclosed in Fig. 42 of the Co'lpitts and Blackwell arti/Wl supra. The low pass filter LPF if., of the type disclosed in said Campbell patents. It is designed to pass currents within the voice range between about 20() and 2,000 cycles frequency, and to suppress currents of high# er frequencies as well as the telegi'apli s ig nals below 200- cycles. T he high lpass filter HPF is designed to' pass currents of the' carrier frequency assigned to Ithis channel and of frequencies `within the telegraph side bands. Thus, these two filters separate the received telephone and telegraph signals.

The lowlpass and high pass filters lill) llO be replaced by band filters of the type disclosed in said Campbell patents. The band filter employed in lace of the low pass filter should be design to .pass currents of frcquencies within lthe-voice or "speech range and to suppress currents of all other frequcnciu. 'Th'eband filter emplo ed in place of the high pass filter should lie designed to pas'. currents of the carrier frequency assigned to this channel and currents of the frequencies within both or one of the telegraph side bands and to suppress currents of all ,other frequencies.

The rectifier R1 may be of anykwell-known type, such, forl example, aspthatfdisclo'sed in Fig. 42 of the Colpitts and Blackwell article, supra.

`The operationv of the-system in so farv as transmission 'and reception 'of telephone signals are "concerned, is well known.` Therell fore no description thereof will be given.

Figl 3 shows awset of curves representing the magnitudes of the transmitted Waves of different frequencies.` Curve A shows the magnitude lof the carrier waves when the telegraph key 6 is open, curve B the 'magnitude ofthe carrier waves when the telegraph key i's closed, and curve C -the magnitude of the voice side hand waves.

Fig. 4 shows the characteristic curve of the' rectifier R1. The curve D is plotted with input voltages Ec as -abscissae against rectified currents In as ordinates.- iV-hen the tele- -graph key is open, 'the input voltage a irnpressed upon the rectifier `causes. rectified current of mav ftude w to How; and when the telegraph ey is closed, thev input voltage b impressed upon the" rectifier causes rectified current of magnitude Y to flow'.

The operation of 'the telegraph channelsuperimposed 'upon the telephone channel and lemployving the saine, carrier fre uency maybe explained b reference to ig'. 4. When the tele aph ey 6 is open, the normal amount o carrier current is flowingto line and the amountof rectifier current through the telegraph receiving relay 8 at the distant station is suiiic'ient to hold its contact, closed, thereby maintaining thek circuit of the sounder 9 closed. When the'telegraph'key 6 is closed the amount of carrier fed to line is reduced as indicated in Fig.43 andthe amount of rectified current through the receiving relay 8 at the distant station is reduced to such an extent that the relay can no longer hold u -its armature; The circuitxof the soun er 9 is therefore opened. When the'tele'graph key 6 is again.l opened, the amount of rectifiedpcurrent through the receiving relay 8 at the distant station increases and it thereupon closes its contact, causing the energization' of the. sounder 9.

, The amplitude` of the side ,bandfrequenf cies (as indicated in Fig.- 3)` is low'com 'ared to the difference between the amplitu es of Isigned to pass currents of the connected tothe main line ML throughl sfelective circuit ICF, which may be either an ordinary tuned circuit comprlsing capacity and inductance er a band filter ofthe type disclosed in the Campbellpatents, supra. If., the selective circuit is a bandvfilter it should` be designed to *pass currents of the frequency assigned to thi'schannel and currents of the frequencies Within one cr kboth side bands thereof 'and to suppress currents of al1 other fre uencies.

kT e interconiniuuicating associated therewith ateach 'tion a transmitting. channti TIG and t receiying channel RIC.. v

The transmitftrg channel TIC ieades a high freque source, such ashun ps1- cillator IO, su 'ing current of ein# rier frequency fil-'ssi output circuit ef thel oscillator 'includes a work circuit connectedfto a transformer 10,

whose secondary terminates in (normally,

o en contacts.,` The connection of the os'- cillator IO to the main line is controlled by a relay 11 having in'its operating circuit a normally open transmitting key 12.

Manuel has,

'The receiving channel RIC `includes an Y input transformer v13, a rectifier IR, and a receiving relayv14 which controls the operan tionA o'f a sounder 15.

`At eachj of the repeater station'sthere is provided forthe intercommunicating channel transmitting and receiving apparatus to be described presently.

Pilot chan-nel.

The pilot channel PC includes a source of high frequency currents PO connected to the main line through a selecting circuit PCF, which may be either a simpleAtuned circuit or aband filter of the Campbell type ,depilot frequency and-to'suppress currents o ll other fre uencies. v v

T re Apilot channelv PC will be described further in connection. with the attenuation `indicator, to be referred yto more in detail hereinafter; l

y Repeater ytilfafto'n.

Each repeater' station Rv is provided with a repeater having two asymmetric repeating channels RNV and Rllwfor-rcpeatug currents inopposite directions. and the transn'litting and receiving apparatus for the intercommunicating channel.

l Repeater. y p The repeater per se, which formsno part 1,413,357,l April 18,1922,

of the present. invention may be of the type disclosed in U. S. patent to Raibourn, No.

or of the type disclosed in my copending application, Serial 210,610,643, filed May 22, 1923. l

Each4 of the "repeating channelsinclu'des an input filter, an amplifier, and an output filter, for further details of which reference should be madeto either the Raibourn patent or my copending application aforesaid.

I ntercommanicatfhcg channel apparatus.

The transmitting and receiving apparatus for the intercommunicating channel is .connected in shuntwith the receiving channels through selective circuits VVICF and EICF so as not to be affected by or affect the op eration of the repeater. Apparatus is pro- -vided for receiving signals from either di- 20 rection over the line. Thus, signals transmitted over the mtercommumcatlng` channel from the west, lme section' are received by a rectifier WR, having a relay 16 in its` and EICF are similar to the selecting cir-` cuit ICF described in connection with the terminal apparatus and perform the same.

Operation of the receiving relay 16 causes the operation of relays 21 and 22." The operation of the relay 21 causes the operation of 'the telegraph sounder 23. The operation of relay 22 disconnects the rectifier ER from the east line section, and connects to this line section Ia sourceof high frequency current IO of the carrier frequency assigned to the intercommunicating channel. When the receivingl relay '17 operates it causes the operation of relays 25 and 19. Relay 25 controls the operation of the sounder 23. The

.operation of relay 19 disconnects rectifier WR from the line, and connects to the line the high frequency source 10. The load on the oscillator 10 1s always constant due to lcarrier signaling systems 'S2 and S3 termlthe provision of resistances 24'an`d`26 connected lthrough closed contacts og relays 22 and 19 respectively to the oscillator. 4 Vixen either relay operates, its associated resista.

'f lance is disconnected from the oscillator and one of themline sections substituted therefor.

The apparatus for the intercommunicatI`l ing channel at each repeater station includes also a telegraph key 27 and a-relay 2S. Whose current IO is connected to both sections of 'l the transmission line outgoingfrom the' repeater station.

at terminal stationW` desir-v ingtowcommunicate withanyA or all of the 'lhe attendant repeater attendants or the attendant at the distant terminal station may do so by actuatlng transmitting key 12 to transmit a carrier. wave modulated in accordance 'with a telegraph signal. Upon the closure-of the liey, relay 11 operates, connecting the source of, high frequency. currents IO to the main line through the selecting circuit ICF. The

lcurrents so impressed upon the lineare selected at the first repeater station-'by the selecting circuit WICF, and ass through the primary Windinv of trans ormer ,18. The resulting induced currents in the .secondary of this transformer are impressed upon the rectifier WR and the rectified current in the output circuit thereof causes the opera-tion,- of relay 16. Relay l16,--1-:i1 operating, causes source IO is selected by the selecting' circuit WICF at the next repeater station where the apparatus functions in the manner 'previously described. Thus, the telegraph signals are relayed from station to station and cause the operation of the sounder ateach of the repeater stations and lthe sounder at the distant terminal station E corresponding to the sounder 15 at station W. Any one of y 's the repeater attendants may likewisecommunicate with the other repeater attendants and terminal attendants by actuating key 27V to transmit the intercommunicating channel' frequency modulated in accordance with telegraph signals.

- Attenuation. 'indicator mechanism.

As already explained, the multiplex carrier telephone and telegraph system of Figs.

land 2, represented as a whole by reference y characters SI, is provided with a pilot channel over which a pilot 'frequency is either continuously or periodically transmitted for controlling the attenuation'indic'ator mechay. I

nism.

Fig. 2 vindicates two additional multiplex nating at the terminal station E. These two systems, S2 and S',may be of the same type as system 'Sl1 shown in detail in Figs. 1 and 2 and previously described. 'These two indicated systemsfare provided with pilotcha-nnels'lzikejthat shown and described in connection with the system S1. Attenuation indicator mechanism -AIM located at the terminal station E may be associated with the transmission line offany-one of the lao , nal station.

The transmission lines of the various multiple-x signaling systems terminating at the station E may be and usually are of differ.

ent lengths. An adjustable resistance network RN is therefore associated with each of the systems so that upon adjustment thereof, the equivalent length may be made the same for all of the transmission lines.

The attenuationindicator mechanism includes means for automatically and successively connecting itself to the transmission lines of the multiplex signaling systems terminating at station E. The indicator mechanism when: connected to one of the transmission ylines responds to variations in strength of thcL received pilot frequency and controls an indicator, the actuation of which indicates the general condition of the net attenuation of the line. For this purpose the indicating mechanism employs a kind yof potentiometer circuit, the condition of balance or unbalance of which determines the4 direction and extent of adjustment necessary to bring the net attenuation ofA the transmission line back to the adopted standard.

The potentiometer circuit includes a galvanometer 30 for indicating the balanced or unbalanced condition of the circuit. The relation between this galvanometer and the indicator controllers is secured through the medium of an automatic controlling apparatus generally indicated at 31.

This controlling apparatus of itself forms no part'of the resent invention and has not been illustrat in detail since it may comprise any suitable Vor well-known arrangement by which a ower shaft such as 32 1s held stationary w en the galvanometer 30 is in its zero 'or' mid-position and is automatically rotated in one direction or the other dependent lupon the direction of 'de- ,flection of the galvanometer. Such rotation persists continuously or by steps until the galvanometer is again brought to its zerol Onev specific 'system for accom.

position. plishng this is shown in UL" S. patent to ABrewegNo. 1,356,804 of October 26, 1920,

and for a more complete description of the circuits and mechanism involved this patent may be referred to. The controlling apparatus31 includes a motor 33 which whenits circuit is closed is driven continuously from a source of power 34.. i

The galvanometeg 30 in seriesvwith a portion of potentiometer 34 is connected across bridge points of a Wheatstone bridge cnr-- cuit 35 which has connected thereto a battery 36 through an adjustable resistance 37. The potentiometer 34 is connected to the output circuit of a rectifier 38. The platecathode path of rectifier 38 forms one arm of a lWheatstone bridge circuit whose other arms are formed by resistances 39, l4Q and 41. The rectifier plate circuit battery 42 is connected across this Wheatstone bridge circuit. The rectifierl input circuit is coupled by means of transformer 43 to the output circuit of'an amplifier 44 whose input cirv cuit is connected tothe terminals: of Aa potentiometer 45. One terminal and an adjustable contact'46of the potentiometer 45 are connected to conductors 47 and 48 multipled to normally open contactsvof relays 49, 50 and 51 by whlch the attenuation in-y dicator mechanism iscconnected Ato the respective transmission lines.

When the attenuation indicator,A mecha' nism AIM is connected to one of the transmission lines, and the attenuation of such line is normal, the grid potential of amplifier 44 will be normal. Consequently the cathode-anode impedance of rectifier 38 will be such as'to set up a certain potential difference across potentiometer 34. The movable contact may then be adjusted vuntil the potential difference due to the rectifier across points c and b. ofthe Wheatstone bridge circuit 35 Vequals the potential difference across the same points due to battery 36. The battery 36 is yso poled that these potential differences are opposite,i whereby the galvanometer 30V will remain in its zero or mid-position. This particular type of rectifier circuit forms no part of the present invention but is disclosedl and claimed in Patent No. 1,579,708, dated Apru- 6,1926. The potentiometer winding 45 is carried by a disc 52 fastened to and rotatable with the shaft 32. The shaft 32 also carries two cams 53 and 54 which respectively control indicator lamps 55- and 56, the circuits" offwhich include a relay v57' for opening the motor circuit and closing the circuit of an audible signal l58. The motor 33 is provided with a'shaft 59 which is rotated continuo j, while the motor is operating. This sha carries a plurality of cams C1, C2, C3 and C4 which'are staggered angularly so that only one of such cams is operative at a time t9 close contacts controlled thereb ThereA is one of these cams for each of t 1e multiplex signaling systems S'S2 and S3. Cam C1 controls relay 49 and its associated signal lamp 60. Cam C2 controls the relay 50l and its associated signal' lamp 61. Cani C3 controls relay 51 and its associated signal lamp Relay 49 thereupon operates to connect the transmission linevML of system S1 to the conductors 47 and 48 extending to the po ftentiometer 45 and amplifier' 44. At the time relay 49operates, signal lamp 60'v is lighted to indicate to vthe attendant that the attenuation indicator mechanism is connected to system S1.

' Y "Such'yrotation of-the shaft 32 causes the ro-l..

If, due to a change in line attenuation or to other causes, the net attenuation of the Isystem isfbelow normahvthe amount of ener from the transmission line ML delivere to the amplilier 44 will be'less than n ormal. Consequently the cathode-anode impedance of rectifier 38 will be greater than The shaft 32 "ed-'from rits zero osition.

tation" of the disc 52 carrying the potentiometer 45 and the contact-46 is shifted :along lthepotentiometer soas to increase the input energy of the amplifier 44. If lthe energy 'incoming from the line is but slightly below normal there' will be but a slight adjustmentof potentiometer 45 and the attenuation indicator mechanism will be disconnected from the system Sl-without further .portions of the indicator mechanism coming into play.

However, ifthe amount of energy incoming, from the transmlsslon line Y1s considerably less than normal, there willbe such an a justment of potentiometer 45 that the cam 54 will close its contact, thereby lighting the indicating lamp 56 and causing the energization of relay 57. Relay 57 upon operating, opens the motor operating circuit ,and causes the operation of the audible signal 58. The' operation of the audible signal 58 is an audible indication to the attendant that the apparatus of the transmission line LIL of the connected system needs adjustment. The lightingof the lamp 56 indicates to the attendant that the adjustment must be in a directionV to increase the gain of the repeater to compensate for the increased attenuation of the line; The lighting of lamp 60 indicates to the attendant that the necessary adjustment must be made along the transmission line of system S1. The particular setj ting ofthe potentiometer 45 at the time`the motor 33 stops, indicates to the attendant roughly the amount of adjustment necessary to bring the attenuation of the system back to the adopted standard.

The attendant at the terminal station E may thereupon communicate with the repeater attendants by means olf-theintercommunicating channel previously described, and instruct such repeater attendants to ymake thc necessary adjustments.

After the adjustments have-` been made and the system S1 thereby restored to normal transmission efiiciency the attendant at' terminal station E may again start the morelay 57. While the shaft 32 is being rotated to cause cam 54 to open its contact, the potentiometer 45 is being varied toward its position corresponding to normal line attenuation.

If the amount of energy incoming from the line is -above normal, there will be such a deflection ofthe galvanometer 30 as will cause the counter-clockwise movement of shaft 32. If the amount of energy incoming from the line is sullicient,the shaft 32 will continue its counter-clockwise movement until cam 53 closes its contact. The lamp `55 thereupon lights and lrelay 57 operates to stop the `motor and voperate the audible signal58.4 j'

If when system S1 is connected to the indicator mechanism, the incoming energy is not sufficient to cause either of the cams 53 or 54 to closeits contact, the motor will not be stopped but will continue to rotate shaft 59. 'The continuous rotation of` the shaft 59 will cause cam C1 to open its contact, 'thereby disconnecting the system S1 56 are necessary, the motor will continue to operate and cam C2 will open itsfcontact. System S2' is thereby disconnected from thc indicator mechanism and subsequently cam C3 closes its contact `.to cause the operation of relay 5i'wh'ch connects system to the indicator mechanism. f J

The relays'49, 50 and 51 are provided With normally closed contacts which are connected in series; `The circuit including these normally closed contacts is connected in shunt of the galvanometer 30,. so that when none of the transmission lines isrconnected to the indicator mechanism the gal vanometer 30 is short-circuited. Consequently, there is vno deflection of the galvanometer 30 due to the unbalance of the Whea'tstone bridge circuit 35 when no transmission ,lineI is connected to the indicator mechanism.

The invention set forth herein is, of

apparatus thereat for indicating the attenu-- y ation on a connected line, and means vfor automatically and successively connecting` the testing apparatus to the lines,

' terminate at a station, testing apparatus at Y the station, means` for connectingthe testing apparatus to any one of the lines, means included in the testing apparatus responsive `to;currents incoming from the connected line', signaling devices associa-ted with the testing apparatus and controlled by said responsive means to indicate the\condition of,

the line and means controlled by currents incoming from the connected line for controlling the means for connecting the testing apparatus to the lines.

3.111 combination, a plurality of high frequency carrier current transmission lines radiating from a station, a pilot frequency channel associated with each transmissionv line, attenuatlon measuring and lndicatln mechanism common to the lines and locate at the station, and means for vvsuccessively connecting said mechanism to the. lines, said mechanism including means responsive4 `to frequencies transmitted over the pilot chani nel of the connected line and having signaling devices controlled by :said frequency re- ,sponsivemeans to .indicate1 whether the attenuation of the connected line isabove or below a predetermined value.l

4. A plurality of transmission lines converging and terminating ata station, testv ing apparatus thereat, switching means-for successively connecting said testing apparatus to said lines,- signaling devices controlled by said switchin means to indicate the particular line ,to wlich said testing apparatus is connected, 4and means for controlling said switching means by currents incoming from the connected line.

5. A plurality oi transmission lines of variable attenuation converging' and termina'ting at a station, an attenuatlon indicator thereat, means for successively, connecting said attenuation' indicator to said lines, and

means including said indicator to selectively indicate an increase lor decreasein the attenuation ofthe connected line.

6. A plurality of transmission lines of variable attenuation converging and terminating at a station, an attenuation indicator thereat, and means for successively connecting said attenuation indicator to said lines,

saidl indicator including a signaling/device` to indicate abnormal attenuation conditions,

on the 'connected line, and a signaling defor connecting the testing apparatus, to the vice to indicate the particular-.character ofgv such abnormal conditlons.

mitted, an indicator common to said lines,

means including a pluralit of relays ,for successively connecting said lndicator to said. lines, means including said indicator responsive to the pilot wave transmitted over the connected line to indicate the condition of said line, and means controlled'by said relays for disabling said indicator when said indicator visnot connected to any o f said lines. i v

8. In a system of transmission regulation, a plurality of transmission lines of variable attenuation -over which pilot waves are transmitted, testing -ap aratus', switching means for connecting said testing apparatus to any one of said lines, signaling devices' controlled by said switching means to in-l dicate the particular line to'which said testing apparatus 4is connected, means including the testing apparatus responsive to the pilot wave incoming over the connected line, and signaling devices `associated with said testing apparatus and controlled by said responsive means to indicatethe condition oftheline. 9.- A plurality of transmission lines converging and terminating at a station, test-` ing a paratus at the station for indicati.

ing t e attenuation on a connected line, means for automatically and successively connecting said a paratus to the lines, and means controlled Ey currents incoming from the connected line for controlling the means lines. A f 95 l0. A plurality of transmission lines com.; f verging and terminating atasta-tion, test,- ing apparatus at the station for indicating the attenuation on a connected line, means y for automatically'connecting the testing ap- 10o paratus to the lines,`,sign'alling devices, and

means controlled by currents incoming from the connected line for controlling the means :for connecting the ttng apparatus to the lines 'and for controlling said signaling de- 105 l vices.

' In witness whereof, I hereunto subscribe my name this 17th day of July A. D., 1923.

JACOB s. Jai/nana. 

